Hydrogen to Heavy Metal Ratio (H/HM ratio)
Posted by Syeilendra Pramuditya on May 4, 2009
Hydrogen to Heavy Metal Ratio or H/HM for short, is a typical parameter in neutronic analysis of nuclear reactor, or more specifically, the Pressurized Water Reactor (PWR) type. Basically it is simply the ratio of moderator (water) to fuel/fissile material (U/Pu/Th) within one calculation cell. I will briefly show you how to calculate this H/HM.
Consider a standard Westinghouse PWR fuel: cylindrical fuel rod array, arranged in rectangular geometry, please refer to this link for the detail of its technical specifications.
Next, make sure that you have understood how to calculate the atomic number density, or otherwise learn it first from the following link:
Now suppose that the fuel has enrichment level of 3%, and 95% theoretical density, hence the atomic number densities are as follow:
Atomic number density of Uranium in the fuel: NU = NU235 + NU238 = 2.3227E+22 atoms/cc
Atomic number density of Hydrogen in the moderator (water): NH = 3.3456E+22 atoms/cc
And the volume fractions are as follow:
Fuel : 33.501 %
Coolant : 54.943 %
Structure : 11.555 %
And finally the H/HM ratio is calculated as follow:
That’s all, easy huh..?